The present invention relates generally to a method for making phase change material, and more particularly, but not by way of limitation, to a low-cost, continuous method of manufacturing form-stable phase change material.
Published reports show that incorporation of paraffinic Phase Change Material (PCM) in building envelopes (wall boards, attic insulation, etc.) can reduce energy consumption by 20+%.
Although paraffins with melting points between 10° C. to 50° C. have all found specialty passive energy storage applications (ranging from clothing to spacecraft thermal systems), the paraffins of interest for building envelopes are those that undergo solid-liquid phase change (melting and freezing) at indoor comfort temperatures (generally between 18° C. and 28° C., or between 64° F. and 82° F.). Such paraffins are also referred to as wax.
Relatively large amounts of energy are stored during paraffin phase change (about 100 to about 240 J/g), thus reducing the peak energy demand for cooling (summer) and heating (winter).
Paraffins offer advantages over other types of PCM due to thermo-oxidative stability and material compatibility (i.e. non-corrosive).
Paraffin wax has traditionally been encapsulated for PCM use, mainly to prevent leakage of paraffin when it is in melt phase. A PCM product that keeps its form whether in solid or melt phase is referred to as form-stable PCM. Other methods of making form-stable PCM involve filling small cups (or other container) with the PCM, capping the filled cups, and incorporating them into building construction material.
Encapsulation is a costly batch process often involving use of toxic monomers. Similarly, filling and capping containers can be labor intensive and inefficient for mass production.
Given the current state of PCM manufacturing technology, PCM products have been too expensive and not broadly available. As such, despite demonstrated potential for improving energy efficiency of residential and commercial buildings, PCM products have not penetrated this, or other cost-focused segments of industry.
Recent studies have shown that form-stable PCMs can be formed by mixing paraffins with high density polyethylene (HDPE). However, there has been no suggestion of how these form-stable PCMs can be manufactured commercially.
To this end, there is a need for a low cost continuous process to manufacture form-stable PCMs. It is to such a process of manufacturing form-stable PCMs that at least one embodiment of the present invention is directed.
The process uses equipment that is well-suited for automated, high production rate, low cost operation.
PCM pellets are similar in form to more costly micro-encapsulates. Specifically, the pellets are relatively small in size and therefore, have a high surface area to volume ratio for increased heat transfer rate.